Multi-fuel control system and method

ABSTRACT

A system includes a controller operable to communicate with at least one sensor and an engine. The controller responds to one or more signals received from the sensor and influences engine operation based on determined engine operation threshold limits and information regarding a first fuel and a second, different fuel. The controller is configured to change or maintain engine operation based on the one or more signals compared to the threshold limits, and to change or maintain an engine fuel supply to control specific fuel consumption of at least one of the first and second fuels and to achieve values for the one or more signals in a determined range relative to the threshold limits. The one or more signals indicate an exhaust emissions parameter or at least one of pre-turbine temperature, fuel injection pressure, turbocharger rotational speed, peak firing pressure, rate of pressure rise, or knock intensity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/204,985, filed Aug. 8, 2011, which is a continuation-in-partof U.S. patent application Ser. No. 12/128,034, filed May 28, 2008, nowU.S. Pat. No. 7,996,147, which are both hereby incorporated by referencein their entirety for all purposes.

BACKGROUND

1. Technical Field

Embodiments of the invention relate to a system and method forcontrolling the use of multiple fuels.

2. Discussion of Art

Internal combustion engines may be classified as compression-ignition orspark-ignition engines. A diesel engine is a compression-ignitionengine, and a gasoline engine is a spark-ignition engine.

Engines may be classified as either two-stroke or four-stroke. A fourstroke engine includes an intake stroke, a compression stroke, a powerstroke, and an exhaust stroke. During the intake stroke, the engineintroduces fuel and air into a cylinder as its respective piston movesaway from top dead center (TDC) in the cylinder. During the compressionstroke, the piston moves toward TDC in the cylinder, thereby compressingthe fuel/air mixture until ignition. The ignition occurs due to the heatof compression and/or a glow plug in a compression-ignition engine. Theignition occurs due to a spark (e.g., a spark plug) in a spark-ignitionengine.

For either engine type, the combustion of the fuel/air mixture causessignificant heat and pressure in the cylinder during the power stroke,thereby driving the piston away from TDC and creating mechanical outputpower through the crankshaft, transmission, and so forth. During theexhaust stroke, the piston moves back toward TDC, thereby forcing theexhaust out of the cylinder. A two stroke engine operates by combiningthe power stroke with the exhaust stroke, and by combining the intakestroke with the compression stroke.

In each of these engines, a variety of parameters affect the engineperformance, fuel efficiency, exhaust constituents, and so forth.Exhaust constituents include carbon oxides (e.g., carbon monoxide),nitrogen oxides (NOx), sulfur oxides (SOx), unburnt hydrocarbons (HC),and particulate matter (PM). Each engine has threshold values, such asspeed, flow rate, temperature, and pressure associated with the variouscomponents. For example, the threshold values may include in-cylinderpeak firing pressure (PFP), pre-turbine temperature (PTT) of aturbocharger, and turbocharger speed (TRBSPD) of the turbocharger. Aspecific threshold value of a turbocharger is a choke line, which oftenrepresents a threshold limit in the air flow rate or pressure ratiobetween a compressor inlet and exit due to design constraints in thesize of inlets, outlets, passages, and so forth. These engine parameters(e.g., PFP, PTT, and TRBSPD) should be maintained within a thresholdvalue range to avoid failure of the engine power assembly andturbocharger. Also, the compressor choke condition should be avoided toreduce the possibility of turbocharger failure.

It may be desirable to have an engine and/or a controller that differsfrom those that are currently available. It may be desirable to have amethod of operation that differs from those methods of use that arecurrently available.

BRIEF DESCRIPTION

In one embodiment, a system includes a controller operable tocommunicate with at least one sensor and with an engine, and thereby tocontrol operation of the engine. The controller is responsive to one ormore signals received from the at least one sensor and influences theengine operation based on determined engine operation threshold limitsand information regarding a first fuel and a second fuel, wherein thefirst fuel and second fuel are not the same type of fuel. The controlleris configured to change or maintain the engine operation based on theone or more signals received from the at least one sensor compared tothe determined engine operation threshold limits, and the controller isconfigured to change or maintain an engine fuel supply to controlspecific fuel consumption of at least one of the first fuel and secondfuel and to achieve values for the one or more signals in a determinedrange relative to the engine operation threshold limits. The one or moresignals indicate an exhaust emissions parameter or at least one ofpre-turbine temperature, fuel injection pressure, turbochargerrotational speed, peak firing pressure, rate of pressure rise, or knockintensity.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and aspects of the invention are understoodwhen the following detailed description is read with reference to theaccompanying drawings in which like characters represent like partsthroughout the drawings, wherein:

FIG. 1 is a block diagram illustrating a system having a multi-fuelcontrol system coupled to a turbocharged engine in accordance withcertain embodiments of the present technique;

FIGS. 2, 3 and 4 are flow charts illustrating various processes ofoperating a turbocharged engine for use with a plurality of differentfuels in accordance with certain embodiments of the present technique;

FIG. 5 is a graph of fuel injection pressure versus crank angle ofdifferent fuels illustrating the effects of heating the fuel to reducethe fuel injection pressure in accordance with certain embodiments ofthe present technique;

FIG. 6 is a graph of fuel injection pressure versus crank angle ofdifferent fuels illustrating the effects of heating the fuel on the fuelinjection duration in accordance with certain embodiments of the presenttechnique;

FIG. 7 is a graph of heat release rate versus crank angle for differentfuels illustrating the effects of heating the fuel on the combustionduration in accordance with certain embodiments of the presenttechnique;

FIG. 8 is a graph of fuel injection pressure versus crank angle ofdifferent fuels illustrating the effects of increasing the fuelinjection pressure on the fuel injection duration in accordance withcertain embodiments of the present technique; and

FIG. 9 is a graph of specific fuel consumption (SFC) and peak firingpressure (PFP) versus advance angle of an engine for different speeds inaccordance with certain embodiments of the present technique.

DETAILED DESCRIPTION

Embodiments of the invention relate to a system and method forcontrolling the use of multiple fuels. The system may be used to propela vehicle. Suitable vehicles can include a locomotive, an automobile, abus, mining or industrial equipment, or a marine vessel. Alternatively,the system may include a stationary system, such as a power generationsystem having the engine coupled to a generator. The illustrated engineis a compression-ignition engine, such as a diesel engine. However,other embodiments relate to a spark-ignition engine, such as agasoline-powered internal combustion engine.

The multi-fuel system includes at least a first fuel and a second thatis different from the first fuel. While fuel blends are contemplated,e.g., diesel and diesel+additive, as used herein and unless indicatedotherwise by context or language, the term “different fuel” means twofuels that are of different fuel base types. Suitable different fuelsmay be selected from diesel, bio-diesel, natural gas, alcohol, vegetableoil, animal-based oil, synth gas, kerosene, hydrogen, and the like.Suitable alcohols may include methanol, ethanol, propanol, butanol, andother short chain alcohols. A suitable vegetable oil may includerapeseed oil, algal oil, colza oil, soya oil, sun flower oil, hemp oil,and nut oils. As used herein, “fuel ratio” means the amount of a firstfuel relative to the amount of a second, different fuel as the fuels aresupplied to an engine.

In one embodiment, the multi-fuel control system maintains engineoperation parameters within acceptable wear and tear limits and withsome control over other operational parameters, such as engineemissions, performance/power output, or the specific fuel consumption.For example, the multi-fuel control system may reduce specific fuelconsumption (SFC) while maintaining peak firing pressure (PFP),turbocharger rotational speed-turbospeed (TRBSPD), pre-turbinetemperature (PTT), and maximum fuel injection pressure (P_(INJMAX))within acceptable limits (e.g., maximum threshold values or designlimits) in response to use of the different fuels. For example, themulti-fuel control system may enable the system to operate with avariety of standard and alternative fuels. As discussed in detail below,the multi-fuel control system may utilize a variety of control schemesto account for the effects of different fuel characteristics, e.g.,viscosity, compressibility, density, lower heating value (LHV), and soforth. In addition, certain embodiments of the system simultaneouslycontrol various parameters to reduce exhaust emissions, such as nitrogenoxides, particulate matter, hydrocarbons, carbon monoxide, or acombination of two or more thereof.

With reference to FIG. 1, a block diagram illustrates a system 10 havinga multi-fuel control system 12 in accordance with an embodiment of theinvention. The multi-fuel control system is associated with a multi-fuelsource 13 and is coupled to a turbocharged engine 14 that is fueled bythe multi-fuel source. The multi-fuel control system can adjust variousengine parameters to account for fuel characteristics associated withthe different fuel types and/or may select the type of fuel or the fuelratio of the fuel types from the multi-fuel source to achieve a desiredengine operation state. This may enable the engine to operate with aplurality of different fuels while using the fuels in a plurality ofratios and combinations to achieve a desired engine operational state.

As illustrated, the engine system includes a turbocharger 16, anintercooler 18, a fuel injection system 20, an intake manifold 22, andan exhaust manifold 24. The illustrated turbocharger includes acompressor 26 coupled to a turbine 28 via a drive shaft 30. The systemalso includes an electrical generator 32 coupled to the turbine 28 via ashaft 34. In addition, the system may include a wastegate valve 36 andan exhaust gas recirculation (EGR) valve 38 disposed downstream from theexhaust manifold 24. In the illustrated embodiment, the wastegate valve36 is disposed between an upstream side and a downstream side of theturbine 28. The illustrated EGR valve 38 is disposed downstream from theexhaust manifold 24 and upstream from the compressor 26. As discussed infurther detail below, the generator 32, the wastegate valve 36, and/orthe EGR valve 38 may be selectively engaged to control parameters of thesystem to account for different fuel characteristics. For example, theelectrical generator 32 and/or the wastegate valve 36 may be selectivelyengaged to reduce the speed of the turbine, thereby reducing the speedof the compressor, reducing the manifold air pressure (MAP), providing aricher fuel/air mixture and decreasing the peak firing pressure (PFP).Similarly, the EGR valve 38 may be selectively engaged to reduce thespeed of the turbine, while also adding heat and recirculating a portionof the exhaust gases into the air intake.

The illustrated system further includes a fuel supply system 40 coupledto the fuel injection system 20. The fuel supply system optionally mayinclude a plurality of fuel tanks corresponding to the different fueltypes, associated fuel pumps, heat exchangers, and associated conduitsas needed for specific implementations (none shown). A conduit 47couples the multi-fuel source to the fuel injection system 20. Ifpresent, the heat exchanger may use the heat of the exhaust gas (orother heat source) to heat the fuel. Heating the fuel may reduce theviscosity, affect the density, and/or induce a phase change. The fuelpump and the heat exchanger may vary the fuel supply pressure, the fuelflow rate(s), and the fuel supply temperature(s) to account forcharacteristics of the different fuels. For example, if one fuel is moreviscous than an another fuel, then the multi-fuel control system mayengage the heat exchanger to increase the fuel supply temperature of theviscous fuel to reduce the viscosity and fuel injection pressure. Byfurther example, the multi-fuel control system may engage the fuel pumpto increase the fuel supply pressure to reduce the fuel injectionduration. In either case, the multi-fuel control system may control thepump and the heat exchanger to maintain the maximum fuel injectionpressure (P_(INJMAX)) within design limits or below threshold values,while also improving the specific fuel consumption (SFC). The control ofthe pump 44 and the heat exchanger 46 also may be used to control thefuel injection in a manner that changes the fuel/air mixture, fuel/fuelratio, combustion duration, peak firing pressure (PFP), peak firingtemperature (PTT), exhaust emissions constituent profile, and so forth.

The system also includes an engine controller 48, e.g., an electroniccontrol unit (ECU), having a multi-fuel control 50 as part of themulti-fuel control system. The engine controller is coupled to varioussensors and components throughout the system, such that the multi-fuelcontrol (and the control system as a whole) can respond to the effectsof different fuels used in the engine. More specifically, as discussedfurther below, the multi-fuel control responds to various sensedparameters to identify possible critical conditions (e.g., approachingor exceeding limits) and take corrective actions to avoid suchconditions. However, in the absence of these conditions, the multi-fuelcontrol may improve specific fuel consumption (SFC). The improved SFCcan be total for the whole engine, or can be for one of the fuelspreferentially over the other fuel(s). In the illustrated embodiment,the engine controller is coupled to and configured to control the pump,the heat exchanger, the fuel injection system, the EGR valve, thegenerator, and the wastegate valve.

In various embodiments, the sensors may include fuel sensors, fuelinjection sensors, engine intake sensors, engine combustion sensors,engine exhaust sensors, turbocharger sensors, and so forth. The fuelsensors may include a fuel supply pressure sensor, a fuel supplytemperature sensor, and a fuel type supply sensor. The fuel injectionsensors may include a fuel injection pressure sensor, a fuel injectionflow rate sensor, a fuel injection timing sensor, and a fuel injectionduration sensor. The engine intake sensors may include an air intaketemperature sensor and an air intake pressure sensor. The engine exhaustsensors may include an exhaust temperature sensor, an exhaust pressuresensor, and exhaust pollutant sensors. The exhaust pollutant sensors maysend a signal to the controller that is operable to determine an exhaustemission parameter, which may include concentrations of nitrogen oxide,particulate matter, hydrocarbons, carbon monoxide, and/or otherpollutants. The engine combustion sensors may include a peak firingpressure (PFP) sensor and a peak firing temperature (PFT) sensor todetect peak conditions within a combustion chamber of the engine. Insome examples, the peak firing pressure sensor may also be used todetermine a rate of pressure rise within a combustion chamber of theengine. In an example, the engine combustion sensors may also include aknock sensor to detect knock intensity of the combustion chamber. KnockIn other examples, knock intensity may be determined from a pressuretrace based on output from the peak firing pressure sensor or othersuitable pressure sensor. The turbocharger sensors may includetemperature sensors, pressure sensors, and speed sensors for both thecompressor 26 and the turbine 28.

In the illustrated embodiment of FIG. 1, the system intakes air into thecompressor through a conduit 52 as illustrated by arrow 54. In addition,as discussed further below, the compressor may intake a portion of theexhaust from the exhaust manifold though a conduit 56 via control of theEGR valve 38 as indicated by arrow 58. In turn, the compressorcompresses the intake air and the portion of the engine exhaust andoutputs the compressed gas to the intercooler via a conduit 60 asindicated by arrow 62. The intercooler functions as a heat exchanger toremove heat from the compressed gas as a result of the compressionprocess. The compression process may heat up the intake air and theportion of exhaust gas. This may be cooled prior to intake into theintake manifold. The compressed and cooled air passes from theintercooler to the intake manifold via a conduit 64 as indicated byarrow 66.

The intake manifold then routes the compressed gas into the engine. Inaddition, the fuel supply system provides the different fuels to thefuel injection system, which in turn provides the fuel into thecylinders of the respective piston cylinder assemblies of the engine.The engine then compresses this mixture of fuels, exhaust gas, and airwithin various piston cylinder assemblies. The controller may controlthe fuel injection timing of the fuel injection system, such that thefuel is injected at the appropriate time into the engine.

In response to changes in the delivered fuel (e.g., different fuelcharacteristics), the multi-fuel control may adjust various aspects ofthe engine operation. The engine operation aspects that the multi-fuelcontrol may adjust include the fuel injection timing, the fuel injectionduration, the fuel supply pressure, the fuel supply temperature, thefuel injection flow rate, or the like. For example, as mentioned above,the engine controller may adjust the fuel supply rate of one or both ofthe different fuels. These adjustments may account for different fuelcharacteristics, such as viscosity, compressibility, density, lowerheating value (LHV), and so forth. The multi-fuel control may change thefuel ratio of the first fuel to the second fuel supplied to thecylinder, and then respond to sensed engine operation parameters so thatthe change in the fuel ratio does not damage the engine or othercomponents of the system. For example, if the multi-fuel control simplymade a 1:1 swap of a low energy fuel for a high energy fuel, theresulting increase in peak pressure in the cylinder may cause damage.Accordingly, as the energy content of the fuel supplied to the cylinderis changed, the multi-fuel control makes corresponding changes to otheraspects of the system—such as, the amount of air being delivered, theinjection duration, the injection timing, and the like. The converseeffect may be provided by the multi-fuel control. That is, if theoperation of the engine may cause damage, the multi-fuel control maychange the fuel ratio, flow rates, or fuel types to place the engineoperation into a safer envelop that is less likely to cause enginedamage.

If the engine is a compression-ignition engine, then the heat of thecompressed air ignites the fuel as each piston compresses a volumewithin its corresponding cylinder. If the engine is a spark-ignitionengine, then a spark ignites the fuel as each piston compresses a volumewithin its corresponding cylinder. In either case, the combustion of thefuel leads to the peak firing pressure (PFP) and peak firing temperature(PFT) within the volume between each piston and its correspondingcylinder. A change in the supplied fuel characteristics (fuel type,ratio, or amount) can cause changes in the combustion process, includingincreases or decreases in the peak firing pressure (PFP) and peak firingtemperature (PFT). The multi-fuel control can adjust a variety ofparameters to account for these changes in the combustion process. Thiscan maintain the combustion process within design limits or belowthreshold values to avoid engine or system damage, or other undesirableeffect.

The multi-fuel control also can reduce or minimize specific fuelconsumption (SFC). The fuel consumption can be the total fuel consumed,or can be weighted to prefer one fuel type relative to another fueltype. For example, the multi-fuel control may adjust fuel injectiontiming, injection duration, fuel flow rates, fuel ratios, and enginespeed to affect the fuel consumption rate. The multi-fuel control candetermine if the peak firing pressure (PFP) is not greater than a designlimit or threshold value, and if not then can put the engine in a firstoperating mode. But, if the peak firing pressure (PFP) is greater thanthe threshold value the multi-fuel control may retard the fuel injectiontiming. This may reduce engine wear and minimize engine damage, but thismay be at the cost of a higher fuel consumption rate.

The engine exhausts the products of combustion from the various pistoncylinder assemblies through the exhaust manifold. The exhaust from theengine then passes through the conduit 68 from the exhaust manifold tothe turbine. The exhaust gas drives the turbine, such that the turbinerotates the shaft and drives the compressor. The speed of both theturbine and the compressor depends on the pressure and flow rate ofexhaust gas. In certain conditions, the system diverts a portion of theexhaust gas away from the turbine via the conduit 56 to the EGR valve 38and/or a conduit 70 to the wastegate valve, as illustrated by arrows 72and 74, respectively. As a result, the diversion of exhaust gas causes adecrease in speed of both the turbine and its driven compressor. Asdiscussed further below, this exhaust gas diversion may be employed toreduce the rotational speed of the turbocharger, reduce the manifold airpressure (MAP), provide a richer fuel/air mixture, provide a differentfuel ratio of the first fuel relative to the second fuel, and reduce thepeak firing pressure (PFP) to account for different fuelcharacteristics. In addition, the generator may load the turbine,thereby effectively reducing the turbospeed in response to themulti-fuel control signal based at least in part on the fuelcharacteristics. The exhaust gas passes out of the turbine and thewastegate valve via conduit 76, as indicated by arrow 78.

FIG. 2 is a flowchart illustrating a process 100 for operating an enginewith different types of fuels in accordance with certain embodiments ofthe present technique. In certain embodiments, the process 100 may be acomputer-implemented process, e.g., executable on the multi-fuel control50 of the engine controller as illustrated in FIG. 1. Thus, the process100 may include various code, instructions, lookup tables, databases,and the like, disposed on a computer-readable medium, such as memory ofthe multi-fuel control. In addition, the multi-fuel control mayimplement the process at least partially by interfacing with a pluralityof sensors distributed throughout the system. For example, themulti-fuel control may receive operational data from sensors distributedthroughout the engine, the turbocharger, the fuel injection system, thefuel supply system, the intake manifold, the exhaust manifold, theexhaust lines, and the like. The multi-fuel-control may implement theprocess by acquiring real-time operational data from the system,evaluating the data against stored data (e.g., databases, lookup tables,threshold values, equations, etc.), and outputting appropriate controlsignals to the components in the system. For example, as discussed indetail below, the multi-fuel-control may implement the process to reduceexhaust emissions, reduce specific fuel consumption (SFC), and maintainthe components within design limits or below threshold values for anyselected fuel.

As illustrated, the process includes control of one or more parametersto account for characteristics of a fuel to enable fuel independentengine operation (block 102). For example, block 102 may include controlsteps to account for viscosity, compressibility, density, lower heatingvalue (LHV), among other fuel characteristics. Thus, block 102 mayinclude changing the fuel supply temperature, the fuel supply pressure,the fuel supply flow rate, or a fuel ratio. The process 100 alsoincludes a control block 104 to reduce specific fuel consumption (SFC).In certain embodiments, the control block 104 also may control variousparameters to reduce one or more emission parameters, such as nitrogenoxides, particulate matter, hydrocarbons, carbon monoxide, or acombination thereof. The process 100 further includes a control block106 to reduce an in-cylinder peak firing pressure (PFP) to stay below alimit. At control block 108, the process 100 may reduce a turbospeed(TRBSPD) and/or prevent a choke condition (i.e., stay below a limit). Atcontrol block 110, the process may reduce a maximum fuel injectionpressure (P_(INJMAX)) to stay below a limit. In certain embodiments, thecontrol blocks 104, 106, 108, and 110 are interrelated with one anotherand the initial control block 102. In other words, a variety of controlmeasures may be taken to control the SFC, PFP, TRBSPD, and P_(INJMAX),alone or in combination with one another.

These control measures may include control of the fuel supply system,the fuel injection system, the turbocharger, and so forth. For example,as mentioned above, the control measures may include increasing ordecreasing the fuel supply temperature, the fuel supply pressure, thefuel ratio, the fuel supply flow rate, or a combination thereof, viacontrol of fuel pumps. In certain embodiments, the change intemperature, pressure, and flow rate causes a change in the pressure,duration, and quantity of each fuel during a fuel injection or cylindercycle, thereby altering the fuel/fuel and fuel/air mixtures, thecombustion duration, the peak firing pressure (PFP), and so forth. Thecontrol measures also may include advancing or retarding the fuelinjection timing (e.g., advance angle) relative to the top dead center(TDC) position of the piston in the cylinder. In certain embodiments,the control measures may advance fuel injection timing to reduce thespecific fuel consumption (SFC) and/or increase the peak firing pressure(PFP). Alternatively, the control measures may retard fuel injectiontiming to reduce the peak firing pressure (PFP) to stay within thedesign limits. By further example, the control measures may includediverting exhaust from the turbine 28 via the wastegate valve 36 and/orthe EGR valve 38, thereby reducing the TRBSPD, reducing the manifold airpressure (MAP), increasing the fuel/air mixture (i.e., more fuel perair), and reducing the peak firing pressure (PFP). The control measuresalso may include engaging the electrical generator 32 to add a load ontothe turbine 28, thereby reducing the TRBSPD, reducing the manifold airpressure (MAP), increasing the fuel/air mixture (i.e., more fuel perair), and reducing the peak firing pressure (PFP). Alternatively, thecontrol measures may reduce the diversion of exhaust gases and/ordisengage the generator 32 to provide the opposite results. Again, avariety of control measures may be taken to maintain parameters withindesign limits or below threshold values. This may be done while reducingspecific fuel consumption (SFC) for each different fuel used with theengine, or by preferentially using one or the other fuel of thedifferent fuel types.

FIG. 3 is a flow chart illustrating a process 120 of operating an enginewith a plurality of different fuels in accordance with certainembodiments of the present technique. In certain embodiments, theprocess may be a computer-implemented process, e.g., executable on themulti-fuel control of the engine controller as illustrated in FIG. 1.Thus, the process may include various code, instructions, lookup tables,databases, and the like, disposed on a computer-readable medium, such asmemory of the multi-fuel control. In addition, the multi-fuel controlmay implement the process at least partially by interfacing with aplurality of sensors distributed throughout the system. For example, themulti-fuel control may receive operational data from sensors distributedthroughout the engine, the turbocharger, the fuel injection system, thefuel supply system, the intake manifold, the exhaust manifold, theexhaust lines, and the like. Thus, the multi-fuel-control may implementthe process by acquiring real-time operational data from the system,evaluating the data against stored data (e.g., databases, lookup tables,design limits, equations, etc.), and outputting appropriate controlsignals to the components in the system. For example, as discussed indetail below, the multi-fuel-control may implement the process to reduceexhaust emissions, reduce specific fuel consumption (SFC), and maintainthe components within design limits or within a determined range ofthreshold values for any selected fuel.

As illustrated, the process includes a first control block 122 to selecta fuel from a plurality of different fuels, such as diesel, gasoline,marine fuel, vegetable oils, biodiesel fuels, and so forth. The processalso includes control blocks 124, 126, 128, and 130 to acquire variousparameters and characteristics to control the engine in response to theselected fuels. Again, as mentioned above, these various parameters maybe acquired from at least one of a database, a lookup table, a sensor,or the like. Thus, the acquired data may correspond to previously storeddata as well as real-time operation data.

For example, block 124 obtains fuel characteristics such as viscosity,compressibility, density, and lower heating value (LHV). Block 126obtains fuel injection parameters, such as fuel injection timing, fuelinjection pressure, fuel injection temperature, fuel injection flowrate, fuel injection duration, and so forth. Block 128 obtainscombustion parameters, such as peak firing pressure (PFP), peak firingtemperature (PFT), combustion duration, rate of pressure rise, knockintensity, exhaust emission parameters, and so forth. Block 130 obtainsturbocharger parameters, such as the rotational speed of theturbocharger, inlet and outlet temperatures, inlet and outlet pressures,and other desired parameters, of the compressor, the turbine, or both.At block 132, the process proceeds to determine threshold values, suchas engine threshold values, fuel injector threshold values, manifoldthreshold values, turbocharger threshold values, knock threshold values,and so forth. For example, the threshold values may correspond to peakpressures, peak temperatures, peak speeds, and so forth. At block 134,the process compares each parameter against a corresponding thresholdvalue. For example, block 134 may compare an actual peak firing pressure(PFP) against a threshold value. Similarly, block 134 may compare anactual rotational speed of the turbocharger against a correspondingrotational speed threshold value. Furthermore, block 134 may compare anactual maximum fuel injection pressure against a pressure thresholdvalue. Block 134 may additionally or alternatively compare an actualrate of pressure rise to a rate of pressure rise threshold value,compare an actual knock intensity to a knock intensity threshold value,compare an actual pre-turbine temperature to a pre-turbine temperaturethreshold value, and/or compare an actual exhaust emission parameter toan exhaust emission parameter value. These are merely examples ofpotential comparisons of parameters with their respective thresholdvalue. At block 136, the process proceeds to control one or morecomponents to maintain parameters within a range of acceptable thresholdvalues independent of the fuel. Again, as discussed above with referenceto FIG. 2, the process may adjust a variety of operational parameters tocontrol the SFC, PFP, TRBSPD, knock intensity, exhaust emissionparameter, rate of pressure rise, and P_(INJMAX), alone or incombination with one another. In one example, knock intensity greaterthan the knock intensity threshold limit may result in injection timingof one or more of the fuels being adjusted, e.g., retarded.

FIG. 4 is a flow chart illustrating a process 140 of operating an engineto account for the effects of changing fuels in an engine in accordancewith certain embodiments of the present technique. In certainembodiments, the process may be a computer-implemented process, e.g.,executable on the multi-fuel control of the engine controller asillustrated in FIG. 1. Thus, the process may include various code,instructions, lookup tables, databases, and the like, disposed on acomputer-readable medium, such as memory of the multi-fuel control. Inaddition, the multi-fuel control may implement the process at leastpartially by interfacing with a plurality of sensors distributedthroughout the system. For example, the multi-fuel control may receiveoperational data from sensors distributed throughout the engine, theturbocharger, the fuel injection system, the fuel supply system, theintake manifold, the exhaust manifold, the exhaust lines, and the like.Thus, the multi-fuel-control may implement the process by acquiringreal-time operational data from the system, evaluating the data againststored data (e.g., databases, lookup tables, threshold values,equations, etc.), and outputting appropriate control signals to thecomponents in the system. For example, as discussed in detail below, themulti-fuel-control may implement the process to reduce exhaustemissions, reduce specific fuel consumption (SFC), and maintain thecomponents within threshold values for any selected fuel.

As illustrated, the process includes a control block 142 to determinefuel supply pressure (P_(FUEL)) and fuel temperature (T_(FUEL)). Forexample, the control block 142 may include monitoring a fuel pressuresensor and a fuel temperature sensor in the fuel supply system asillustrated in FIG. 1. The process also includes a control block 144 todetermine a lower heating value (LHV), density, compressibility, and/ormaximum fuel injection pressure (P_(INJMAX)). In certain embodiments,the control block 144 may automatically sense a fuel types and accessthe fuel characteristics for those fuel types from a lookup table.

Alternatively, the process may include user input to acquire the fuelcharacteristics. For example, a user may enter or select one or morefuel types and the fuel characteristics can be retrieved from a lookuptable. In addition, the control block 144 may sense or monitor one ormore of the fuel characteristics, such as the fuel injection pressure(P_(INJMAX)) during operation of the engine. The process includes acontrol block 146 to determine a fuel injection duration and acombustion duration. For example, the control block 146 may includesensors to calculate a beginning, an end, and thus a duration of thefuel injection and the combustion. In certain embodiments, the controlblock 146 may estimate the fuel injection duration and/or the combustionduration based on other parameters, such as stored data, sensed data,equations, and so forth. At control block 148, the process 140 proceedsto determine an in-cylinder peak firing pressure (PFP), a rotationalspeed of the turbocharger-turbospeed (TRBSPD), and a pre-turbinetemperature (PTT). Again, the control block 148 may include a pressuresensor, a speed sensor, a flow rate sensor, and a temperature sensor tomonitor and acquire each of these values during operation of the engine.

At query block 150, the process evaluates whether the peak firingpressure (PFP) is greater than a limit. If the peak firing pressure isnot greater than the limit at block 150, then the process proceeds toadvance injection timing and/or reduce engine speed to reduce thespecific fuel consumption (SFC) at control block 152. In addition toreducing the specific fuel consumption (SFC) at control block 152, theabove control measures may cause an increase in the peak firing pressure(PFP). If the peak firing pressure is greater than the limit at block150, then the process proceeds to query block 156 to evaluate additionalparameters against respective limits. At query block 156, the processevaluates whether or not the turbospeed (TRBSPD) is greater than a limitor the pre-turbine temperature (PTT) is greater than a limit. If theselimits are not exceeded at query block 156, then the process proceeds toretard the injection timing at control block 158. By retarding theinjection timing, the control block 158 reduces the peak firing pressure(PFP). As appreciated, in certain embodiments, this control block 158may be performed directly in response to query block 150 when the peakfiring pressure (PFP) is greater than a limit.

If the rotational speed of the turbocharger (TRBSPD) is greater than acorresponding rotational speed limit or the pre-turbine temperature(PTT) is greater than a corresponding temperature limit at query block156, then the process 140 responds accordingly. Suitable responsesinclude proceeding to change the fuel flow rate of one or more of thefuel types, derate the engine, change the engine speed, or change themanifold air pressure (MAP), or a combination thereof, at control block160. For example, as discussed above, the control block 160 may reducethe speed of the turbocharger (TRBSPD) by diverting exhaust gases viathe wastegate valve and/or the EGR valve, or by adding a load via thegenerator, or a combination thereof. In turn, the reduced speed of theturbocharger 16 may cause a decrease in the manifold air pressure (MAP),an increase in the fuel/air mixture (i.e., more fuel per air), and soforth. Furthermore, in certain embodiments, the process may providecontrol measures opposite from block 160 if the limits are not exceededat query block 156, thereby supplementing or replacing the controlmeasures shown in the control block 158.

The process proceeds to query block 162 for an evaluation of fuelinjection characteristics. At query block 162, the process evaluateswhether or not the maximum fuel injection pressure (PINJMAX) is greaterthan a limit. If the limit is not exceeded at query block 162, then theprocess proceeds to decrease a fuel temperature (TFUEL) and/or increasea fuel supply pressure (PFUEL) at block 164. Otherwise, if the limit isexceeded at query block 162, then the process proceeds to increase thefuel temperature and/or decrease the fuel supply pressure at controlblock 166. At this point, the process of the illustrated embodimentrepeats as illustrated by blocks 168 and 170.

FIG. 5 is a graph 200 of fuel injection pressure versus crank angle fordifferent fuels illustrating the effects of heating the fuel on the fuelinjection pressure in accordance with certain embodiments of the presenttechnique. As illustrated, plot 202 illustrates a first fuel without anyheating by a heat exchanger. Plots 204 and 206 illustrate a second fueldifferent from the first fuel, wherein plot 204 illustrates the fuelwithout heating and plot 206 illustrates the fuel with heating (e.g.,100 degrees Celsius).

As illustrated by comparison of plot 202 and 204, the second fuel has agreater maximum fuel injection pressure (PINJMAX) relative to the firstfuel as illustrated by arrow 208. However, without heating, both thefirst and second fuels have very similar fuel injection durations asillustrated by the plots 202 and 204. With heating (e.g., 100 degreesCelsius), the second fuel has a reduced maximum fuel injection pressure(PINJMAX), which is closer to that of the first fuel as indicated byarrow 210. Thus, as illustrated by the graph 200, the second fuel may beheated in accordance with one of the described multi-fuel controlsystems or methods to reduce the maximum fuel injection pressure(PINJMAX) to stay within a range of threshold values.

FIG. 6 is a graph 220 of fuel injection pressure versus crank angle fordifferent fuels illustrating the effects of heating the fuel on the fuelinjection duration in accordance with certain embodiments of the presenttechnique. In the illustrated embodiment, plot 222 corresponds to afirst fuel without heating, while plot 224 illustrates a second fuelwith even more heating than described above. Similar to the embodimentdiscussed above with reference to FIG. 5, the first fuel may be dieselfuel and the second fuel may be natural gas. In the illustratedembodiment, the second fuel may be heated from a cryogenic or liquidstate to a gaseous state. As shown, the first fuel of plot 222 has afuel injection duration as indicated by arrow 226, while the second fuelof plot 224 has a fuel injection duration indicated by arrow 228. Theillustrated fuel injection duration 228 of the heated second fuel 224 isgreater than the fuel injection duration 226 of the unheated first fuel222. However, the heated second fuel of plot 224 has a lower maximumfuel injection pressure (P_(INJMAX)) than the unheated first fuel ofplot 222, as indicated by arrow 230. This is due to second fuel beingheated more than necessary. As a result, the fuel heating associatedwith the previously described multi-fuel control systems and methodsresulted in a lower maximum fuel injection pressure (P_(INJMAX)) and agreater fuel injection duration in the embodiment of FIG. 6.

FIG. 7 is a graph 240 of heat release rate (HRR) versus crank angle fordifferent fuels illustrating the effects of heating on the combustionduration in accordance with certain embodiments of the presenttechnique. As illustrated, plot 242 corresponds to a first fuel withoutheating and plot 244 corresponds to a second fuel with heating and aftera phase change. As illustrated in FIG. 7, the heat release rates of thefirst and second fuels begin at about the same crank angle but end atdifferent crank angles as illustrated by the horizontal shift on theright portion of plot 244 relative to the plot 242. The first fuel ofthe plot 242 has a combustion duration illustrated by arrow 246, whilethe second fuel of the plot 244 has a combustion duration generallyillustrated by arrow 248. As illustrated, the combustion duration 248may be greater than the combustion duration 246. In addition, themaximum heat release rate of the first fuel of plot 242 is greater thanthe maximum heat release rate of the second heated fuel of plot 244 asindicated by arrow 250. Again, in accordance with the previouslydescribed multi-fuel control systems and methods, the temperature of thesecond fuel of plot 244 may be varied to change the heat release rate,the combustion duration, and the associated peak firing temperature(PFT) during the combustion process, thereby adapting the second fuel tothe limitations of the engine.

FIG. 8 is a graph 260 of fuel injection pressure versus crank angle ofdifferent fuels illustrating the effects of fuel supply pressure on themaximum fuel injection pressure (P_(INJMAX)) and the fuel injectionduration in accordance with certain embodiments of the presenttechnique. As illustrated, the graph 260 includes a plot 262corresponding to a first fuel and plots 264 and 266 corresponding to asecond fuel. Specifically, as discussed in the previous embodiments ofFIGS. 5-7, the first fuel may correspond to a diesel fuel, and thesecond fuel may correspond to a vegetable oil, such as palm oil. In theillustrated embodiment, the plot 264 corresponds to the second fuelwithout an increase in the fuel supply pressure. In contrast, the plot266 corresponds to the second fuel with an increase in the fuel supplypressure, e.g., 1600 bar. As illustrated by plots 262 and 264, thesecond fuel of plot 264 has a relatively lower maximum fuel injectionpressure than the first fuel of plot 262, as indicted by arrow 268.However, the second fuel of plot 264 also has a relatively greater fuelinjection duration than the first fuel of plot 262 as indicated byarrows 270 and 272, respectively. These differences between the firstand second fuels can be changed by varying the fuel supply pressure ofthe second fuel, as illustrated by the changes between the plots 264 and266 of the second fuel. With reference to plots 262 and 266, the fuelinjection duration of the first and second fuels are substantially thesame and the second fuel has a greater maximum fuel injection pressure(P_(INJMAX)) than the first fuel as indicated by arrow 274. Thus, inaccordance with certain aspects of the previously described multi-fuelcontrol systems and methods, the fuel supply pressure of the second fuelmay be increased to both reduce the fuel injection duration and increasethe maximum fuel injection pressure (P_(INJMAX)) to adapt the secondfuel to the design limits of the engine.

FIG. 9 is a graph 280 of specific fuel consumption (SFC) and peak firingpressure (PFP) versus advance angle for different engine speeds of afuel in accordance with certain embodiments of the present technique.The advance angle may be defined as the angle before top dead center(TDC) at which fuel injection begins. In the graph 280, plots 282 and284 correspond to the specific fuel consumption (SFC) at first andsecond engine speeds, respectively. In addition, plots 286 and 288correspond to the peak firing pressure (PFP) at the first and secondengine speeds, respectively. The graph 280 further illustrates a peakfiring pressure (PFP) limit, such as a design limit, as indicated byhorizontal line 290. In the embodiment of FIG. 9, the fuel illustratedby plots 282, 284, 286, and 288 may correspond to the same second fuelas illustrated in FIGS. 5-8. For example, the fuel may correspond to avegetable oil, such as palm oil. In general, the plots 282 and 284illustrate a decrease in the specific fuel consumption (SFC) with anincrease in the advance angle. In contrast, the plots 286 and 288illustrate an increase in the peak firing pressure (PFP) with anincrease in the advance angle. As a result, the specific fuelconsumption (SCF) and the peak firing pressure (PFP) are inverselyproportional relative to one another. At the first speed of the engine,the specific fuel consumption (SFC) is relatively high and the peakfiring pressure (PFP) is relatively low as illustrated by plots 282 and286. However, as mentioned above, an increase in the advance anglecauses both an improvement in the specific fuel consumption (SFC) andalso an increase in the peak firing pressure (PFP) as illustrated byplots 282 and 286. Unfortunately, the peak firing pressure (PFP) of plot286 eventually reaches the peak firing pressure (PFP) limit 290.

Accordingly, the previously described multi-fuel control systems andmethods may be employed to reduce the engine speed from the first speedto the second speed as represented by plots 284 and 288. As a result ofthe reduced engine speed, the peak firing pressure (PFP) shifts upwardfrom the plot 286 to the plot 288. However, the graph 280 illustratesthat an advance angle 292 may be selected by the control system toprovide a reduced specific fuel consumption (SFC) and a peak firingpressure (PFP) close to but below the limit 290, as indicted by anintersection 294 of the plots 284 and 288.

FIG. 9 illustrates a variety of adjustments that can be taken tomaintain the peak firing pressure (PFP) below the limit 290, while alsominimizing the specific fuel consumption (SFC). Again, the previouslydescribed multi-fuel control systems and methods may increase the enginespeed from the second speed to the first speed, retard the fuelinjection timing (i.e., reduce the advance angle), or a combinationthereof. Conversely, if the peak firing pressure is below the limit 290,then the previously described multi-fuel control systems and methods mayadvance the fuel injection timing (i.e., increase the advance angle), orreduce the engine speed from the first speed to the second speed, or acombination thereof. Although graph 280 illustrates exemplary techniquesto reduce the specific fuel consumption (SFC) and maintain the peakfiring pressure (PFP) below the limit 290, other embodiments of themulti-fuel control system and method may adjust other parameters of thesystem of FIG. 1 to optimize the engine for the particular fuel.

Technical effects of the disclosed embodiments of the invention includethe operability a combustion-engine system (e.g., system) with aplurality of different fuels in a controlled manner that reduces exhaustemissions, reduces specific fuel consumption (SFC), and maintainscomponents/parameters within design limits. In other words, thetechnical effects of the disclosed embodiments of the invention includean engine that is fuel independent, i.e., not limited to one specificfuel. As discussed above, the technical effect of a fuel independentengine may be achieved by making various controls dependent on the fuelcharacteristics, thereby adjusting operation of the engine to accountfor the different fuel characteristics to reduce exhaust emissions,reduce specific fuel consumption (SFC), and maintaincomponents/parameters within design limits. The technical effects may becarried out by a computer-implemented method or system, such asillustrated in FIGS. 1-4 and described in detail above. For example,each step, decision block, or the like, as shown in FIGS. 2-4 maycorrespond to a computer instruction, logic, or software code disposedon a computer readable or machine readable medium. By further example,the computer-implemented methods and/or code may be programmed into anelectronic control unit (ECU) of an engine, a main control system of avehicle (e.g., a locomotive unit), a remote control station thatcommunicates with the vehicle, or the like. In certain embodiments, thecomputer-implemented method or system may be programmed into themulti-fuel control of the engine controller (e.g., electronic controlunit) shown in FIG. 1.

For example, in certain embodiments as described above, a system mayinclude a computer readable medium (e.g., control 50 of FIG. 1) and code(e.g., processes 100, 120, or 140 of FIGS. 2-4) disposed on the computerreadable medium, wherein the code comprises instructions to adjust oneor more parameters affecting operation of an engine to account fordifferent fuel characteristics of a plurality of different fuels. Thecode may include instructions to control a specific fuel consumption,and instructions to control at least one of a peak firing pressure, apre-turbine temperature, a turbospeed, or a maximum fuel injectionpressure. The system also may include at least one of an engine controlunit having the computer readable medium, an engine having the computerreadable medium, or an engine powered vehicle having the computerreadable medium.

An embodiment relates to a system. The system comprises a controlleroperable to communicate with at least one sensor and with an engine, andthereby to control operation of the engine, wherein the engine isoperable with a first fuel and a second fuel, the first fuel and thesecond fuel not being the same type of fuel. The controller isconfigured to change or maintain the engine operation based oninformation regarding the first fuel and the second fuel, and furtherbased on one or more signals received from the at least one sensorcompared to the determined engine operation threshold limits, and thecontroller is configured to change or maintain an engine fuel supply tocontrol specific fuel consumption of at least one of the first fuel orthe second fuel and to achieve values for the one or more signals in adetermined range relative to the engine operation threshold limits. Theone or more signals indicate at least one of an exhaust emissionsparameter or one or more of a pre-turbine temperature, a fuel injectionpressure, a turbocharger rotational speed, a peak firing pressure, arate of pressure rise, or a knock intensity.

The controller is operable to change a fuel flow rate to the engine ofthe first fuel relative to the second fuel, and thereby to change a fuelratio of the first fuel relative to the second fuel. The exhaustemissions parameter is based on at least one exhaust componentcomprising nitrogen oxide, particulate matter, hydrocarbon, or carbonmonoxide.

The engine operation threshold limits may include a pre-turbinetemperature threshold limit, a fuel injection pressure threshold limit,a turbocharger rotational speed threshold limit, a peak firing pressurethreshold limit, and/or a rate of pressure rise threshold limit.

The controller is operable to derate the engine, decrease engine speed,or decrease a manifold air pressure in response to a sensed measurementthat a turbocharger rotational speed is greater than the turbochargerrotational speed limit. The controller is operable to at least one ofadvance fuel injection timing or decrease engine speed if a peak firingpressure is not greater than the peak firing pressure limit. Thecontroller is operable to at least one of retard fuel injection timingor increase engine speed if the peak firing pressure is greater than thepeak firing pressure limit.

The knock intensity may be inferred by a pressure trace or measured by aknock sensor. The first fuel may comprise diesel fuel and the secondfuel may comprise natural gas.

The controller is operable to control for the first fuel, the secondfuel, or for both the first and second fuels supplied to the engine atleast one of: fuel injection timing, fuel supply pressure, fuel supplytemperature, fuel supply rate, or a ratio of the first fuel to thesecond fuel.

The controller is operable to control at least one of manifold airpressure or engine speed in response to the one or more signals receivedfrom the at least one sensor during combustion of the at least one ofthe first or the second fuel.

The controller is operable to vary one or more of fuel injection timing,fuel supply pressure, fuel supply temperature, fuel ratio, manifold airpressure, engine speed, or EGR rate.

The controller is operable to change or maintain the engine operation asthe one or more signals are compared to the engine operation thresholdlimits, and the controller is configured to change or maintain theengine fuel supply to achieve values for the one or more signalsreceived from the at least one sensor in a determined range relative tothe engine operation threshold limits and to reduce specific fuelconsumption of one or more different fuels of the at least first fueland second fuel.

The controller is operable to supply simultaneously to the engine two ormore of a plurality of fuels so that the engine operation is maintainedbelow a peak firing pressure limit and a turbocharger rotational speedlimit, and engine operation further is based on one or more of the rateof pressure rise, the knock intensity, the pre-turbine temperature, or amaximum fuel injection pressure to be within determined, correspondingengine operational threshold limits, and thereby to reduce the totalspecific fuel consumption. The two or more of the plurality of fuels mayinclude the first fuel, the second fuel, and/or other fuels.

Another embodiment of a system includes a controller operable tocommunicate with at least one sensor and with an engine, and thereby tocontrol operation of the engine, wherein the engine is operable with afirst fuel and a second fuel, the first fuel and the second fuel notbeing the same type of fuel. The controller is configured to change ormaintain the engine operation based on information regarding the firstfuel and the second fuel, and further based on one or more signalsreceived from the at least one sensor compared to determined engineoperation threshold limits, and the controller is configured to changeor maintain an engine fuel supply to control specific fuel consumptionof at least one of the first fuel or the second fuel and to achievevalues for the one or more signals in a determined range relative to theengine operation threshold limits, where the one or more signalsindicate knock intensity.

The controller is operable to vary one or more of fuel injection timing,fuel supply pressure, fuel supply temperature, fuel ratio, manifold airpressure, engine speed, or EGR rate.

The controller is operable to control for the first fuel, the secondfuel, or for both the first and second fuels supplied to the engine atleast one of: fuel injection timing, fuel supply pressure, fuel supplytemperature, fuel supply rate, or a ratio of the first fuel to thesecond fuel.

One or more specific embodiments of the invention will be describedbelow. In an effort to provide a concise description of theseembodiments, all features of an actual implementation may not bedescribed in the specification. It should be appreciated that in thedevelopment of any such actual implementation, as in any engineering ordesign project, numerous implementation-specific decisions must be madeto achieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

When introducing elements of various embodiments of the invention, thearticles “a,” “an,” “the,” and “said” are intended to mean that thereare one or more of the elements. The terms “comprising,” “including,”and “having” are intended to be inclusive and mean that there may beadditional elements other than the listed elements. Any examples ofoperating parameters and/or environmental conditions are not exclusiveof other parameters/conditions of the disclosed embodiments.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to one ofordinary skill in the art. It is, therefore, to be understood that theappended claims are intended to cover all such modifications and changesas fall within the scope of the claimed invention.

What is claimed is:
 1. A system, comprising: a controller operable tocommunicate with at least one sensor and with an engine, and thereby tocontrol operation of the engine, wherein the engine is operable with afirst fuel and a second fuel, the first fuel and the second fuel notbeing the same type of fuel; wherein the controller is configured tochange or maintain the engine operation based on information regardingthe first fuel and the second fuel, and further based on one or moresignals received from the at least one sensor compared to determinedengine operation threshold limits, and the controller is configured tochange or maintain an engine fuel supply to control specific fuelconsumption of at least one of the first fuel or the second fuel and toachieve values for the one or more signals in a determined rangerelative to the engine operation threshold limits, wherein the one ormore signals indicate at least one of an exhaust emissions parameter orone or more of: a pre-turbine temperature, a fuel injection pressure, aturbocharger rotational speed, a peak firing pressure, a rate ofpressure rise, or a knock intensity.
 2. The system of claim 1, whereinthe controller is operable to change a fuel flow rate to the engine ofthe first fuel relative to the second fuel, and thereby to change a fuelratio of the first fuel relative to the second fuel.
 3. The system ofclaim 1, wherein the exhaust emissions parameter is based on at leastone exhaust component comprising nitrogen oxide, particulate matter,hydrocarbon, or carbon monoxide.
 4. The system of claim 1, wherein theengine operation threshold limits include a pre-turbine temperaturethreshold limit.
 5. The system of claim 1, wherein the engine operationthreshold limits include a fuel injection pressure threshold limit. 6.The system of claim 1, wherein the engine operation threshold limitsinclude a turbocharger rotational speed threshold limit.
 7. The systemof claim 6, wherein the controller is operable to derate the engine,decrease engine speed, or decrease a manifold air pressure in responseto a sensed measurement that a turbocharger rotational speed is greaterthan the turbocharger rotational speed limit.
 8. The system of claim 1,wherein the engine operation threshold limits include a peak firingpressure threshold limit.
 9. The system of claim 8, wherein thecontroller is operable to at least one of advance fuel injection timingor decrease engine speed if a peak firing pressure is not greater thanthe peak firing pressure limit.
 10. The system of claim 8, wherein thecontroller is operable to at least one of retard fuel injection timingor increase engine speed if the peak firing pressure is greater than thepeak firing pressure limit.
 11. The system of claim 1, wherein theengine operation threshold limits include a rate of pressure risethreshold limit.
 12. The system of claim 1, wherein the knock intensityis inferred by a pressure trace or measured by a knock sensor.
 13. Thesystem of claim 1, wherein the first fuel comprises diesel fuel and thesecond fuel comprises natural gas.
 14. The system of claim 1, whereinthe controller is operable to control for the first fuel, the secondfuel, or for both the first and second fuels supplied to the engine atleast one of: fuel injection timing, fuel supply pressure, fuel supplytemperature, fuel supply rate, or a ratio of the first fuel to thesecond fuel.
 15. The system of claim 1, wherein the controller isoperable to control at least one of manifold air pressure or enginespeed in response to the one or more signals received from the at leastone sensor during combustion of at least one of the first fuel or thesecond fuel.
 16. The system of claim 1, wherein the controller isoperable to vary one or more of fuel injection timing, fuel supplypressure, fuel supply temperature, fuel ratio, manifold air pressure,engine speed, or EGR rate.
 17. The system of claim 1, wherein thecontroller is operable to change or maintain the engine operation as theone or more signals are compared to the engine operation thresholdlimits, and the controller is configured to change or maintain theengine fuel supply to achieve values for the one or more signalsreceived from the at least one sensor in a determined range relative tothe engine operation threshold limits and to reduce specific fuelconsumption of one or more different fuels of the at least first fueland second fuel.
 18. The system of claim 1, wherein the controller isoperable to supply simultaneously to the engine two or more of aplurality of fuels, the plurality of fuels including the first fuel andthe second fuel, so that the engine operation is maintained below a peakfiring pressure limit and a turbocharger rotational speed limit, andengine operation further is based on one or more of the rate of pressurerise, the knock intensity, the pre-turbine temperature, or a maximumfuel injection pressure to be within determined, corresponding engineoperational threshold limits, and thereby to reduce the total specificfuel consumption.
 19. The system of claim 1, wherein the one or moresignals indicate the knock intensity.
 20. The system of claim 19,wherein the controller is operable to vary one or more of fuel injectiontiming, fuel supply pressure, fuel supply temperature, fuel ratio,manifold air pressure, engine speed, or EGR rate.
 21. The system ofclaim 19, wherein the controller is operable to control for the firstfuel, the second fuel, or for both the first and second fuels suppliedto the engine at least one of: fuel injection timing, fuel supplypressure, fuel supply temperature, fuel supply rate, or a ratio of thefirst fuel to the second fuel.
 22. A system, comprising: an engineoperable with a first fuel and a second fuel, the first fuel and thesecond fuel not being the same type of fuel; at least one sensor; acontroller operable to communicate with the at least one sensor and tocontrol the engine; wherein the controller is configured to change ormaintain operation of the engine based on information regarding thefirst fuel and the second fuel, and further based on one or more signalsreceived from the at least one sensor compared to determined engineoperation threshold limits, and the controller is configured to changeor maintain an engine fuel supply to control specific fuel consumptionof at least one of the first fuel or the second fuel and to achievevalues for the one or more signals in a determined range relative to theengine operation threshold limits, wherein the one or more signalsindicate at least one of an exhaust emissions parameter or one or moreof: a pre-turbine temperature, a fuel injection pressure, a turbochargerrotational speed, a peak firing pressure, a rate of pressure rise, or aknock intensity.
 23. A vehicle comprising the system of claim 22,wherein the engine is a diesel engine.